Abstract
ABSTRACTMineralized collagen fibrils are composed of tropocollagen molecules and mineral crystals derived from hydroxyapatite to form a composite material that combines optimal properties of both constituents and exhibits incredible strength and toughness. Their complex hierarchical structure allows collagen fibrils to sustain large deformation without breaking. In this study, we report a mesoscale model of a single mineralized collagen fibril using a bottom‐up approach. By conserving the three‐dimensional structure and the entanglement of the molecules, we were able to construct finite‐size fibril models that allowed us to explore the deformation mechanisms which govern their mechanical behavior under large deformation. We investigated the tensile behavior of a single collagen fibril with various intrafibrillar mineral content and found that a mineralized collagen fibril can present up to five different deformation mechanisms to dissipate energy. These mechanisms include molecular uncoiling, molecular stretching, mineral/collagen sliding, molecular slippage, and crystal dissociation. By multiplying its sources of energy dissipation and deformation mechanisms, a collagen fibril can reach impressive strength and toughness. Adding mineral into the collagen fibril can increase its strength up to 10 times and its toughness up to 35 times. Combining crosslinks with mineral makes the fibril stiffer but more brittle. We also found that a mineralized fibril reaches its maximum toughness to density and strength to density ratios for a mineral density of around 30%. This result, in good agreement with experimental observations, attests that bone tissue is optimized mechanically to remain lightweight but maintain strength and toughness. © 2015 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research (ASBMR).
Highlights
Bone is a complex hierarchical composite made of an organic matrix, filled by a mineral phase and water.[1,2] Its structure is organized to achieve remarkable mechanical performance.[3,4] The organic matrix, representing around 25% of bone weight, is constituted of more than 90% of type I collagen molecules that assemble in a quarter-staggered fashion into thin (20 to 500 nm) and long ($100 mm) fibrils.[5,6,7] The remaining 10% of the matrix is composed of noncollagenous proteins
Full atomistic molecular dynamics made it possible to assess the mechanics of collagen molecules and fibrils,(23,24) mineral crystals,(25,26) and their interface.[27,28,29,30] large-scale models have been developed to investigate the interplay between organic collagen molecules and mineral crystals
Further details on the development of the mineralized collagen fibril full atomistic model can be found in Nair and colleagues[32] and Gautieri and colleagues.[33]. The fibril is LARGE DEFORMATION MECHANISMS, PLASTICITY, AND FAILURE OF COLLAGEN FIBRIL 381 built by replication of the tropocollagen molecule and mineral crystal according to the periodicity given by the full atomistic model
Summary
Bone is a complex hierarchical composite made of an organic matrix, filled by a mineral phase and water.[1,2] Its structure is organized to achieve remarkable mechanical performance.[3,4] The organic matrix, representing around 25% of bone weight, is constituted of more than 90% of type I collagen molecules that assemble in a quarter-staggered fashion into thin (20 to 500 nm) and long ($100 mm) fibrils.[5,6,7] The remaining 10% of the matrix is composed of noncollagenous proteins. Other studies based on analytical models have uncovered some key mechanistic features of mineralized tissues where experiments reach their limits, shedding some light on the role of mineral platelets in material strengthening.[13,18,19,20,21,22] These models help link the nanostructure of the tissue to the organ’s mechanical response by integrating some levels of the complex hierarchical structure of bone They cannot be used to explore the relationship between nanostructure, chemical composition, and bone mechanics, in the large deformation regime. Full atomistic molecular dynamics made it possible to assess the mechanics of collagen molecules and fibrils,(23,24) mineral crystals,(25,26) and their interface.[27,28,29,30] large-scale models have been developed to investigate the interplay between organic collagen molecules and mineral crystals
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